linux-kernel - Re: [PATCH] cpufreq: CPPC: Correct desired

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Date:   Wed, 12 Oct 2016 10:33:48 -0700
From:   Hoan Tran <hotran@....com>
To:     "Prakash, Prashanth" <pprakash@...eaurora.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Al Stone <ahs3@...hat.com>, linux-pm@...r.kernel.org,
        lkml <linux-kernel@...r.kernel.org>, Loc Ho <lho@....com>,
        Duc Dang <dhdang@....com>
Subject: Re: [PATCH] cpufreq: CPPC: Correct desired_perf calculation

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Hi Prashanth,

On Wed, Oct 12, 2016 at 8:36 AM, Prakash, Prashanth
<pprakash@...eaurora.org> wrote:
> Hi Hoan,
>
> On 10/11/2016 3:12 PM, Hoan Tran wrote:
>> The desired_perf is an abstract performance number. Its value should
>> be in the range of [lowest perf, highest perf] of CPPC.
>> The correct calculation is
>>   desired_perf = freq * cppc_highest_perf / cppc_dmi_max_khz
>>
>> Signed-off-by: Hoan Tran <hotran@....com>
>> ---
>>  drivers/cpufreq/cppc_cpufreq.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
>> index 1b2f28f..ab1d4b7 100644
>> --- a/drivers/cpufreq/cppc_cpufreq.c
>> +++ b/drivers/cpufreq/cppc_cpufreq.c
>> @@ -84,7 +84,7 @@ static int cppc_cpufreq_set_target(struct cpufreq_policy *policy,
>>
>>       cpu = all_cpu_data[policy->cpu];
>>
>> -     cpu->perf_ctrls.desired_perf = (u64)target_freq * policy->max / cppc_dmi_max_khz;
>> +     cpu->perf_ctrls.desired_perf = (u64)target_freq * cpu->perf_caps.highest_perf / cppc_dmi_max_khz;
> The patch looks good, I suppose we can add a small optimization. We can do a simple check
> to see if the newly computed desired_perf is same as old one, If it is same we can just return
> here instead of calling cppc_set_perf with same desired_perf value.

That's a good point. I can add a check into this patch.

Thanks
Hoan

>
> Thanks,
> Prashanth